Meng-Chyi Wu

Optical properties of GaSb alloys and photodiodes grown by liquid‐phase epitaxy

The carrier concentration of GaSb epitaxial layers grown from Sb‐rich solutions by liquid‐phase epitaxy is controlled by replacing nominally undoped GaSb by Te‐doped polycrystalline GaSb to suppress or compensate the background hole concentration. The dependence of the 10 K photoluminescence peak wavelength and intensity on the doping level of the Te‐compensated GaSb layers has been investigated. The absorption spectra are examined as a function of carrier concentration. Low‐dopant‐concentration p‐type GaSb samples exhibit the band gap shrinkage with increasing hole concentration, while the lightly Te‐doped n‐type GaSb samples exhibit a band gap increase due to the Burstein–Moss shift with increasing electron concentration. By using Te‐doped GaSb layers with an electron concentration of 5.6×1015 cm−3, the fabricated GaSb photodiodes exhibit a low dark current of 2 μA at −5 V, a high breakdown voltage of 28.7 V at 20 μA, and a maximum photoresponsivity of 0.55 A/W with an external quantum efficiency of 40%...

Photoluminescence of high‐quality GaSb grown from Ga‐ and Sb‐rich solutions by liquid‐phase epitaxy

The temperature dependence of photoluminescence from the high‐quality unintentionally doped GaSb layers grown by liquid‐phase epitaxy has been studied. The epitaxial layers grown at temperatures above 590 °C, from the Ga‐ or Sb‐rich solutions, reproducibly have a low‐carrier concentration of 6–8×1015 cm−3 and exhibit p‐type conduction. But it gives n type as grown from the Ga‐rich solution at 360 °C. For the samples grown from the Ga‐rich solutions, the 16 K photoluminescence spectrum is dominated by the partially resolved lines related to the transitions of excitons bound to donors and neutral acceptors. The acceptor‐related band (777.8 meV) which is always presented in the GaSb material due to the native lattice defects has been much reduced as compared to the exciton‐related lines. Especially for the n‐type samples grown at low temperatures (360 °C), the ratio of the emission intensity from the exciton‐related lines to that from the acceptor‐related band is 10. For the samples grown from the Sb‐rich so...

High-Speed GaN-Based Blue Light-Emitting Diodes With Gallium-Doped ZnO Current Spreading Layer

Conventional light-emitting diodes (LEDs) always pursue the high brightness required for solid-state lighting. However, they always exhibit very low frequency bandwidth of tens MHz. In this letter, we investigate the fabrication and characterization of high-speed GaN-based blue LEDs. The frequency response of LEDs is mainly limited by its diffusion capacitance and resistance, and the injected carriers in the active region of the device. Through appropriate device design, gallium-doped Zinc oxide film deposited by atomic layer deposition is used as the top contact layer with high lateral resistance to self-confine the current injection. In addition, a smaller bonding pad is used to reduce the RC time constant. Thus, the GaN-based blue LEDs with a 75-

Flexible fullerene field-effect transistors fabricated through solution processing.

\mu{\rm m}

Anomalous p-channel amorphous oxide transistors based on tin oxide and their complementary circuits

diameter exhibit a 3-dB modulation bandwidth of 225.4 MHz and a light output power of 1.6 mW at the current of 35 mA. Such LEDs can be applied to visible light communication in future.

High-Speed Light-Emitting Diodes Emitting at 500 nm With 463-MHz Modulation Bandwidth

Recent research into organic semiconductors for organic thin-film transistors (OTFTs) – as alternatives to amorphous silicon-based systems – has yielded improved synthetic and fabrication techniques for devices with great potential for the use in consumable electronic applications.[1–3] To realize the advantages of organic semiconductors in practical applications, OTFTs fabricated through solution processing (spin-coating, casting, or printing) on flexible substrates are strongly desired. Although many groups have developed OTFTs incorporating soluble small-molecule or polymer semiconductors, the number of available hole-transporting materials overwhelms the number of electron-transporting materials.[4–6] Preparing efficient organic integrated circuits at low cost requires soluble hole- and electron-transporting materials that ideally exhibit comparable electrical performance. At present, the development of highperformance n-channel OTFTs remains a challenge, especially when using attractive fabrication processes (e.g., solution processing).

Complementary inverter circuits based on p-SnO2 and n-In2O3 thin film transistors

In this article, we report the fabrication of SnO2 thin film transistors (TFTs) fabricated by reactive evaporation. Different from the previous reports, the fabricated TFTs exhibit p-type conductivity in its undoped form. The postdeposition annealing temperature was tuned to achieve p-channel SnO2 TFTs. The on/off ratio and the field-effect mobility were ∼103 and 0.011cm2∕Vs, respectively. To demonstrate inverter circuit, two devices with different threshold voltages were combined and an output gain of 2.8 was achieved. The realization of p-channel oxide TFTs would open up new challenges in the area of transparent electronics.

Influence of doping density on the normal incident absorption of quantum-dot infrared photodetectors

Light-emitting diode (LED) is one of the most important light sources due to its low power consumption and long lifetime. In this letter, we present the high-frequency characteristics of GaN-based green LEDs with different aperture diameters. In order to get higher current density, we use ring-shaped electrode to confine the current injection. Unlike conventional LEDs, we only use its natural feature to get a high modulation bandwidth. The LEDs investigated have a peak emission wavelength of 500 nm. The highest optical 3-dB modulation bandwidth is ~463 MHz at 50 mA for the 500-nm green GaN-based LED with an aperture diameter of 75 μm. It is the highest bandwidth yet reported for the green GaN-based LEDs. The LED also exhibits a relatively high output power of ~1.6 mW at 50 mA as compared with other high-speed LEDs. Such the LEDs can be applied to plastic optical fiber and visible light communication in the future.

InGaAs PIN photodiodes on semi-insulating InP substrates with bandwidth exceeding 14 GHz

Thin film transistors (TFTs) of indium oxide (In2O3) and tin oxide (SnO2) were fabricated on SiO2 gate dielectric using reactive evaporation process. Structural investigation of the films revealed that In2O3 films were polycrystalline in nature with preferred (222) orientation and SnO2 films exhibited amorphous nature. The x-ray photoelectric spectroscopy measurements suggest that SnO2 films were oxygen rich and presume mixed oxidation states of Sn, namely Sn2+ and Sn4+. While the In2O3 based TFTs possess n-type channel conduction, SnO2 based TFTs exhibited anomalous p-type conductivity. Integration of these n- and p-type devices resulted in complementary inverter with a gain of 11.

Vertical organic triodes with a high current gain operated in saturation region

The influences of doping densities at the quantum-dot (QD) region for 30-period InAs∕GaAs quantum-dot infrared photodetectors (QDIPs) are investigated. The InAs∕GaAs QDIPs with a lower doping density can operate at high responsivity and high background-limited-performance temperature. Also observed is the decreasing photocurrent ratio of s∕p-polarized lights for the QDIPs with increasing QD doping density. Compared to the similar photocurrent ratio of s∕p-polarized lights for the GaAs∕AlGaAs quantum-well infrared photodetectors at different applied voltages, the observed voltage-dependent response ratio for QDIPs is attributed to the strong scattering characteristics of QDs occupied with photoexcited electrons for electron transport through the QD region.